Drying roll



March 21, 1939, H R 2,151,048

' DRYING ROLL Filed May 1, 1937 INVENTOR ATTORNEY.

Patented Mar. 21, 1939 DRYING ROLL Howard J. Rowe, Lakewood, Ohio, assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Application May, 1, 1937, Serial No. 140.091

6 Claim.

This invention relates to the manufacture of cellulose material, and more particularly to drying machinery used in such manufacture.

In the course of the manufacture of sheets of 5 cellulose material, such'as that sold under the name Cellophane," it is customary to subject the sheets to a drying and stretching operation.

This is ordinarily doneby passing them over a succession of heated rolls having a somewhat tacky surface or a surface to which the sheets will adhere. The rollsare in the form of metal cylinders mounted to rotate about their longitudinal axes, and maybe heated by any of a number of methods, although the method generally used is to run heated water through them.

Prior to myinvention, iron and steel drying rolls having a coating of varnish have been used for this purpose. However, such rolls have pre-. sented several diiiiculties. The adhesiveness of the varnish coating varieswith the temperature of the roll; the colder the roll is, the less adhesive is its surface, so that it is difiicult to obtain uniform results. Furthermore, the individual I rolls do not heat uniformly throughout, the result being that the drying eiIect of anyone roll on the readily and uniformly than iron or steel. How-.

ever, such rolls have not been'entirely satisfactory, chiefly because of the fact that in the course of its passage through the drying machinery the cellulose material sometimes becomes tangled among the rolls and mustbe cut away with sharp knives which frequently score the aluminum and raise burrs on the roll surfaces. These burrs mar 4 the cellulose sheets which subsequently pass over minum rolls is that their external surface is corroded by the treating solutions present on the cellulose material, and their internal surface may be corroded by the water which heatsthe rolls, if this method of heating is used.

It is an object of my invention to provide an aluminum drying roll for use in the drying and stretching of cellulose films or sheets, the'roll having an external surface which is of a type which will not be susceptible to burring by knife edges when cellulose material must be cut away from the roll. Another object of this invention is to provide an aluminum drying roll having a hard, abrasion-resistant coating consisting substantially of aluminum oxide which has been them. Another difiiculty encountered with aluimpregnated with a binding agent. Other objects of the invention will be apparent from the following specification and claims. and from the accompanying drawing.

I have discovered that aluminum or aluminum base alloy drying rolls which are provided with a suitably treated coatingof the type generally referred to in the art as an oxide coating have properties which make them highly suitable for use in the manufacture of cellulose films or sheets. The term oxide coating is used herein to designate an artificially produced coating consisting substantially of aluminum oxide on aluminum or aluminum base alloys, which coating'is formed by a chemical or electrochemical treatment and is of substantial thickness, as distinguished from the thin film of aluminum oxide which is naturally formed on aluminum surfaces by contact with the air. Such oxide coatings may be produced on aluminum'surfaces by a number of well-known methods, chemical or electrochemical in nature, such as by immersing the article to be coated for a short time in a hot solution of an alkali carbonate containing a small amount of an inhibitor such as a chromate, or by making the article the anode in an electrolytic cell in' which the electrolyte consists of an acid solution such as sulfuric acid, chromic acid, oxalic acid, or mixtures of these acids. The characteristics of the coatings vary somewhat with the methods used to produce them, particularly as to hardness. For my purposes, I prefer to use the methods which produce the harder, more adherent types of coating, and have found especially suitable the method in which the aluminum article to be coated is made the anode in an electrolyte consisting of a 15 percent solution of sulfuric acid, with a current densitypf about 18 amperes per square foot of surface tolae goated. applied to it. However, other methods can also be used satisfactorily, and it will be understood that I do not intend to limit my invention to an oxide coating produced by any particular method.

0xide coatings are ordinarily hard, adherent, abrasion-resistant, and somewhat absorptive or adsorptive. After the aluminum roll has been provided with an oxide coating, I then subject it to a further treatment designed to improve its frictional characteristics. This treatment consists in impregnating the oxide coating with resin or a resinous material, or with an alkali silicate, such as sodiumsilicate. This may be accomplished by applying a solution of the impregnating substance to the oxide coated surface in any suitable manner. as by immersing the said surface in the solution or by spreading the solution on it. In either event, the oxide coating absorbs or adsorbs some of the impregnating material. It is only necessary to apply enough of the solution for the oxide coating to become impregnated with the binding material, and it is not necessary that so much be applied as to form a film or layer over the oxide coating; in fact, after the impregnating material has been applied, I prefer to wipe off any excess remaining on the roll surface, so that the material which is left is resident in the oxide coating. When a water solution of sodium silicate is used, it is also desirable to bake the coating at an elevated temperature, preferably a little above boiling, to drive oif water and make the impregnating material less soluble. If it is desired to increase the frictional resistance of the rolls further than can be done with the above treatment, their surface may be subjected to a suitable roughening procedure prior to applying the oxide coating, as by etching or sand blasting, so long as the roll surface is not roughened to such an extent that the cellulose films are marred during their passage over the rolls.

It may be desirable that the frictional resistance of some of the drying rolls vary from that of other rolls in the drying machinery. This result can readily be accomplished in accordance with my invention by controlling such variable factors as the type of preliminary surface treatment given the rolls, and the, type of impregnating material used.

The invention will be further described with reference to the accompanying drawing, in which a drying roll prepared in accordance with my invention is illustrated, part of the roll being cut away to show the coating.

In the drawing, the drying roll is shown as comprising a hollow aluminum cylinder I having on its external surface a coating 2 consisting substantially of aluminum oxide. It will be appreciated that the thickness of the coating is exaggerated for the purposes of illustration. In actual practice, a, coating of from .0005 to .001 of an inch in thickness is ordinarily suflicient. However, any desired thickness of coating can be used. Although in-the drawing the oxide coating is shown only on the external surface of the cylinder, it will be appreciated that other portions of the roll, such as the interior, may also be coated to advantage.

Drying rolls embodying my invention have 'a hard, abrasion-resistant coating which, though it may be scored by the sharp knives used to cut tangled cellulose material from the machinery, will not burr or develop rough edges. offer proper frictional resistance to the cellulose material passing over them, insuring eflicient drying and stretching of the material, and the material may be readily stripped from them when necessary. Furthermore, since the rolls are made of aluminum, a more uniform distribution of heat is obtained throughout.

As a specific example of my invention, an alu'- minum base alloy drying roll cylinder was provided with an oxide coating by making it the The? anode in an electrolytic cell in whicha' 15 per cent solution of sulfuric acid constituted the electrolyte. A current having a density of 18 amperes per square foot of cylinder surface was applied for 50 minutes, with the electrolyte maintained at a temperature of F. The cylinder was r then removed from the electrolyte, rinsed with water, and dried. Thereafter its external surface was coated with a 25 per cent solution by weight of resin dissolved in ethyl acetate. The surface of the cylinder was then wiped thoroughly to remove the portion of the resin solution which iwas not absorbed or adsorbed by the oxide coat- In another example of the invention, an aluminum base alloy drying roll cylinder was -provided with an oxide coating in the same way as in the previous example. It was then immersed for several minutes in a 10 per cent solution of sodium silicate in water, after which it was taken out of the solution and wiped thoroughly with a cloth to remove the material not adsorbed or absorbed by the oxide coating.

perature of 215 F.

As used hereinabove and in the appended claims the term aluminum includes aluminum and aluminum alloys.

I claim: I

1. A drying roll-for drying cellulosic sheet or film, said roll comprising an aluminum cylinder having on at least part of its surface a hard, adherent, abrasion-resistant coating consisting substantially of aluminum oxide, said coating being impregnated with a binding agent.

2. A drying roll for drying cellulosic sheet or film, said roll comprising an aluminum cylinder having, on at least part of its surface a hard, adherent, abrasion-resistantcoating consisting substantially of aluminum oxide, said coating'bein impregnated with a resinous material.

3. A drying roll for drying cellulosic sheet or film, said roll comprising an aluminum cylinder having on at least part of its surface a hard, adherent, abrasion-resistant coating consisting substantially of aluminum oxide, said coating being impregnated with an alkali silicate.

4. A drying roll for drying cellulosic sheet or It was then heated in an oven for two hours at a temfilm, said roll comprising an aluminum cylinder having on at least part of its surface a hard, adherent, abrasion-resistant coating consisting substantially of aluminum oxide, said coating being impregnated with resin- 5. A drying roll for drying cellulosic sheet or film, said roll comprising an aluminum cylinder having on at least part of its surface a hard, ad-

herent, abrasion-resistant coating consisting sub- HOWARD J. ROWE. 

